New Head-Fier

Thanks for the reply.
I looked at the instruction manual. I'm not finding the files listed there. I only found X3ii_v1.0_9970b2e-181013.zip which has readme.txt and update.upt.
I downloaded the installer from here: https://www.rockbox.org/wiki/RockboxUtility#Download. I chose the Linux 64 bit version.
I started Rockbox but couldn't use the automatic. My player was not found, and couldn't figure out how to do it manually.

Would appreciate help. I've been working on this for some time, but no success.

From what I understood, you have to -
1. Extract the update.upt file from X3ii_v1.0_9970b2e-181013.zip archive
2. Copy the update.upt to the root directory of your micro-sd card and insert it in to the player.
3. Power on the device select the update firmware from dap menu.

I strongly recommend you to verify these steps with one of the members who has previously rockboxed x3ii, to avoid damaging/bricking your device.